<Swing Dev> [9] Review request for 8027639: JComboBox's popup leaves tracks after closing

[Semyon Sadetsky]

Hello,

Please review fix for JDK9:

bug: https://bugs.openjdk.java.net/browse/JDK-8027639

webrev: http://cr.openjdk.java.net/~ssadetsky/8027639/webrev.00/

When the Swing repaint manager paints Swing to a separate off-screen 
buffer the root window is not painted. So in case of non-opaque root 
window having transparent background the repainted buffer area 
transparency is not restored and previously visible Swing components can 
remain visible.

The solution is to paint the root window's background to the repainted 
area in case the root window is non-opaque.

--Semyon